It is necessary for starting a high intensity discharge lamp such as a high-intensity discharge (HID) lamp to use a high-voltage generating device called an igniter. The high-voltage generating device is generally provided in the form of an electromagnetic device such as a pulse transformer for converting a low-voltage input to a high-voltage output of pulsed waveform (as disclosed in, for example, Japanese Patent Laid-open Publications 11-16752 and 11-74132).
One of such conventional electromagnetic devices is shown in structure in FIGS. 65 to 68. A coil bobbin 60 is made of an insulating material such as synthetic resin having substantially a cylindrical shape which comprises two outer flanges 61 at both ends and a partition flange 62 between the two outer flanges 61. A primary winding 63 at the low voltage side is wound between one of the two outer flanges 61 and the partition flange 62 while a secondary winding 64 at the high voltage side is wound between the other outer flange 61 and the partition flange 62. In particular, the secondary winding 64 is fabricated by winding a long, flat rectangular foil conductor with its wider sides facing each other (in the form of, so-called, edge-wise winding) for improving both the edge side insulation and the contact area of windings. Finally, a couple of U-shaped magnetic cores 65 made of Mn—Zn ferrite are inserted and joined to both ends of the coil bobbin 60 with the primary winding 63 and the secondary winding 64, hence forming an electromagnetic device (a pulse transformer).
FIG. 69a is a perspective view of another conventional electromagnetic device and FIG. 69b is a cross sectional view taken along the line A–A′ of FIG. 69a. The another conventional electromagnetic device comprises a bar-like magnetic core 3PA and a coil winding 2 wound as the secondary winding on a coil bobbin 60 thereof mounted on the magnetic core 3PA. For ease of winding the coil winding 2 on the coil bobbin 60 secured to the magnetic core 3PA, a recess 31PA is provided in each end of the magnetic core 3PA to determine its position along the axial direction. A process of fabricating the bar-like magnetic core 3PA having the recess in each end thereof will be explained referring to FIG. 70. The process of fabricating the magnetic core 3PA employs a pair of rods K, each having a projection K1′ for shaping the recess 31PA and a swage die U having a through hole U1 provided therein for insertion of the rods K. As shown in FIG. 70a, the process starts with shaping the magnetic core 3PA using the die U and the rods K. Then, the lower rod K is lifted up to the upper end of the die U as shown in FIG. 70b to remove the magnetic core 3PA from the die U in the direction denoted by the arrow for increasing the efficiency. The magnetic core 3PA may however be injured at the edge R1 of the recess 31PA upon being removed from the die U as shown in FIG. 71.
FIG. 72 is a perspective view of a further conventional electromagnetic device. The electromagnetic device shown is a pulse transformer for converting a low voltage input to a high voltage output as called an igniter to generate a high voltage for energizing a high intensity discharge lamp. The conventional device shown in FIG. 72 comprises a bar-like magnetic core 3PA, a bobbin 4PA, a pair of coil windings 9 and 10 mounted on the bobbin 4PA mounted to the magnetic core 3PA, a casing 5PA made of a resin material for enclosing those components therein, and terminals 6 connected to coil windings 9 and 10 at one end and extending at the other end from the casing 5PA. The coil winding 9 incorporates an insulation coated wire (of round wire) comprising an electrical conductor having a round shape in the cross section and an insulating coating provided over the wire conductor and serving as the primary winding while the coil winding 10 serves as the secondary winding. The coil winding 9 is connected to one (61) of the terminals 6 and the coil winding 10 is connected to another (62).
This conventional electromagnetic device is fabricated by winding the coil windings 9 and 10 on the bobbin 4PA, inserting the magnetic core 3PA into the bobbin 4PA, assembling those in the casing 5PA, connecting the terminals 6 to the corresponding coil windings 9 and 10, and filling the casing 5PA with an amount of epoxy resin (by vacuum filling process).
FIG. 73 is a perspective view of a conventional welding joiner welded to the insulation coated wire. A welding joiner 6PA which can be welded to the insulation coated wire without stripping the insulation coating comprises, as shown in FIG. 73, a flat base portion 61 extending along one direction and a folded portion 62 extending from one side of the base portion 61 at a right angle to the direction and folded along its width at a portion 63 so that the two portions 61 and 62 confront each other. The welding joiner 6PA is preferably utilized as the terminal 6 of the conventional electromagnetic device. One example of this arrangement is disclosed in Japanese Patent Laid-open Publication 11-114674.
It is common that high intensity discharge lamps are widely used as the head lights of vehicles because they are high in the brightness, low in the power consumption, and long in the operating life and thus much favorable in the safety than any halogen lamps. As such high intensity discharge lamps have increasingly been popular, the electromagnetic devices are now desired for minimizing the thickness in view of the dimensional requirements of igniters. However, the conventional devices are hardly reduced in the thickness with the coil bobbin 60 provided between the magnetic core 65 (See FIG. 65) and the coil. Also, there is essentially provided a gap between the coil bobbin 60 and the magnetic core 65 for ease of mounting, thus elongating the distance between the magnetic core 65 and the coil and creating differences in the properties between the electromagnetic devices. Although a modification is proposed where the coil bobbin is replaced by an insulating cover made of a resin material (disclosed in Japanese Patent Laid-open Publication 2000-36416), it retains the same drawbacks.
When the bobbin is provided between the magnetic core and the coil windings, its terminals are fixedly connected to the coil windings. In case of a bobbin-less device, the terminals connected with the coil windings may be secured with much difficulty.
The process of fabricating an electromagnetic device shown in FIG. 72 requires substantially four or more hours for carrying out the major processing steps including preparation, drying, and curing steps. For implementing a scheme of mass production, extra investments for expanding the existing production facility has to be needed. Also, when the epoxy resin vacuum filling process is employed, it may limit the lead-out of the terminals 6 from the casing 5PA to one single direction. This prevents the terminals 6 from being respectively bent and oriented in a desired pattern of the circuitry planning. Since the coil windings of a metallic material create undesired events of spring back, their ends have to be bound together or supported by any proper means. The epoxy resin vacuum filling process may generally develop an interface between the casing 5PA and the epoxy resin material thus allowing a high voltage to leak from the interface. The edge-wise winding may cause the coating of the coil windings to be peeled off when its curvature radius is too small.
The convention welding joiner 6PA may often cause the insulation coated wire to be dislocated when held between the base portion 61 and the folded portion 62 and pressed with a pair of welding electrodes. If worse, the insulation coated wire may completely be slipped off from between the base portion 61 and the folded portion 62. As the welding of the insulation coated wire to the welding joiner is carried out only with poor consistency, it is much desired to modify the welding joiner for improvement of its stable joining function and operational reliability.
The present invention has been developed in view of the foregoing aspects and its object is to provide an electromagnetic device, a high-voltage generating apparatus, and a method for making the electromagnetic device where the dimensional reduction and the improvement of properties are achieved, and the duration of time required for carrying out the production steps is minimized.